The EU must call time on UK Government stalling on Brexit, Sinn Fein’s leader said as she urged Brussels to convene a special summit on the Irish border impasse.

Mary Lou McDonald urged Michel Barnier to push for the additional meeting of European leaders as she met the EU’s chief Brexit negotiator in Brussels.

After emerging from talks with Mr Barnier on Monday afternoon, party president Mrs McDonald said she had received assurances that the EU was standing firm on its insistence that a so-called Irish border “backstop” agreed between Brussels and London must form part of the final withdrawal treaty.

Last December the EU and UK agreed that Northern Ireland would continue to adhere to a number of European customs regulations if a wider Brexit trade deal failed to materialise. It was supposed to be a fallback position that would ensure a free-flowing border regardless of the terms of the UK’s exit from the EU.

However, the two sides are at loggerheads on how to translate that agreement into a legally binding commitment in a potential withdrawal treaty. Recent developments at Westminster have placed further question marks over the backstop, amid claims that Theresa May’s Chequer’s deal and subsequent Brexiteer-driven amendments to Government legislation are incompatible with the December agreement.

Mrs McDonald, who was accompanied in Brussels by Sinn Fein vice president Michelle O’Neill, said an extra EU meeting is required in September to try to forge a resolution ahead of October’s crunch summit – the effective deadline to secure a Brexit deal.

The Sinn Fein leader also criticised Mrs May’s speech in Belfast last week, when the British Prime Minister made it clear that she would not sign up to any backstop that treated Northern Ireland differently to the rest of the UK.

“Last week’s visit by Theresa May to Belfast has raised very serious concerns over the British Government’s approach to Brexit,” Mrs McDonald said in Brussels.

“In December we were told that a ‘backstop’ was a cast-iron guarantee, that the Good Friday Agreement would be protected in word and spirit, and that there would be no diminution of rights for Irish and EU citizens in the North.

“The British Government is seeking to row back on these commitments and to bin the December agreement. Theresa May is placing her personal self-interest to stay in Downing Street ahead of the needs of Ireland, North and South.

“The British Government is now engaged in a game of brinkmanship which puts our all-island economy and our agreements at risk. There is no certainty and no clarity on Irish interests.

“The EU has made clear that without the ‘backstop’ there will be no withdrawal agreement and that the interests of Ireland must be dealt with in line with the December agreement.

“Michel Barnier assured us this remains the case and that Britain must agree workable solutions in line with the December agreement.

“We believe that this must be given affect and the EU should call time on British Government stalling. The EU should hold a special summit in advance of October to resolve Irish issues before closing on the withdrawal agreement.”